REVISED ANISOTROPIC SITE POTENTIALS FOR THE WATER DIMER AND CALCULATED PROPERTIES

Two new parametrizations of a recent ab initio polarizable anisotropic site potential for water are presented, The new versions improve the description of the electrostatic interactions, add an explicit charge- transfer term, and use more accurate dispersion coefficients from the recent literature. To assess the merits of the new models, the potenti al energy surface of the dimer is analyzed and a comparison is made wi th 12 other polarizable potentials for water in the literature, most o f them being currently used in computer simulation. The structure, ene rgy, and harmonic intermolecular frequencies of the stationary paints have been determined and compared with the best available nb initio ca lculations. The energy barriers and pathways for hydrogen atom interch ange within the dimer are discussed. The second virial coefficient B(T ) of steam between 373 and 973 K, including first-order quantum correc tions, is reported. For all the models, the quantum corrections are fo und to be significant at the lowest temperatures, amounting to 10-15% at 373 K, Roughly 90% of the quantum corrections arise from the rotati onal degrees of freedom. Among the potentials considered, only those p resented in the present work and a few others are really successful in reproducing the experimental results for B(T) in that temperature ran ge.